Planographic printing plate and method for preparing same



United States Patent This invention relates to a planographic printingplate and to a method for making such a plate. More particularly, itrelates to a method for preparing a sealed hydrophilic layer or layerson a planographic printing plate and to the plate resulting therefrom.

In the following specification and claims it will be understood allparts and percentages are by weight unless otherwise indicated.

The art of planographic printing depends upon the im' miscibility ofgrease and water and upon the preferential retention of a greasyimage-forming substance by the image areas, and a similar retention ofan aqueous damp- 3,160,506 Patented Dec. 8, 1964 "ice - entirelysatisfactory in that the printing plates produced ening fiuid bynon-image areas. When a greasy image is imprinted on a suitable surface,and the entire surface is then moistened with an aqueous solution, theimage areas will repel the water, and the non-image areas will retainthe water. Upon subsequent application of greasy ink, the image portionsretain the ink, whereas the moist, nonimage areas repel it. The image isthen transferred to paper or cloth, via an intermediate, so calledolf-set cylinder, which is necessary to prevent mirror image printmg. Ip

A planographic printing plate is prepared by coating a suitablesubstratewith a photosensitive emulsion, either by the manufacturer or by thelithographer, and subsequently exposing the thus sensitized plate toactinic light through a photographic image. The exposed plate isthereafter treated to produce oleophilic ink-receptive image portionsand hydrophilic ink-repulsive non-image portions, which may be utilizedto produce plural copies.

Depending upon the nature of the photosensitive emulsion employed, thetreated plate may be utilized to directly reproduce the image to whichit is exposed, in which case it is termed a positive-acting plate, or toproduce an image complementary to that to which it is exposed, in whichcase it is termeda negative-acting plate. In either case the image areasof the photosensitive emulsion are rendered oleophilic by appropriatetreatment and the remaining portion of the emulsion is removed by adesensitizing treatment to define the hydrophilic non-image areas.

It has been known to use, as the base material for photolithographicplates, either a waterproof paper or a flexible sheet of metal. Typicalmetals'which may be used are aluminum, steel, zinc, magnesium, chromiumand copper.

Because paper is relatively coarse grained and has a tendencyto stretch,a plate having a metallic base provides finer reproduction and longerservice than does a paper base plate. In coating a metallic plate with alights'e nsitive material, however, it is necessary to initially providethe metal with a hydrophilic surface to which the lightsensitiveemulsion adheres, which defines the ink-repulsive non-image areas uponremoval of portions of the exposed light-sensitive material. It is knownto produce such hydrophilic surfaces on metallic plates forplanographic.

printing purposes by various procedures. One such procedure is disclosedin copending application Serial No. 44,843, filed on July 25, 1960, nowabandoned, and involves treatment of a metallic surface with a titaniumhexahalide to provide a hydrophilic layer thereon, followed by sealingsuch layer in a hot water bath. This procedure and others heretoforeknown have not been thereby often have limited shelf lives and limitedwaterreceptivity. Moreover such plates tend to absorb moisture and areunsuitable in moist, warm atmospheres, thereby creating packaging andstorage problems under such conditions. o

It is accordingly among the objects of the present invention to providea method for preparing a planographic printing plate having ahydrophilic layer thereon, which plate is stable under relatively highhumidity and temperature conditions.

A further object of the invention is to provide such a method and theresulting printing plate, which is simply and economically produced andwhich may be utilized for relatively long press runs.

These and other objects of the invention will be more clearly understoodfrom the following description thereof.

In accordance with the present invention, a method is provided forpreparing a planographic printing plate which involves treating ametallic surface with a transition metal fluoride, viz., an acid, alkalimetal, or alkaline earth metal salt of the transition metaltetrafluorides, pentafluorides or hexafiuorides, to form a hydrophiliclayer on the metallic surface, sealing such layer with chromic acid andthereafter applying a photosensitive emulsion in superposed relationover'the resulting sealed hydrophilic layer. The thus sensitizedprinting plate is exposed to actinic light defining aphotographic imageand the exposed plate is treated to produce an adhering oleophilic imagethereon which may be utilized to produce plural copies.

Surprisingly, the chromic acid sealed hydrophilic layers thus formed aremarkedly stable under high humidity and temperature conditions, and theresulting plates may therefore be stored for long periods of time under"such conditions. Printing plates having hydrophilic layers sealed byhot water treatments, on the other hand, absorb moisture and break downwhen exposed to 90% relative humidity for periods of from one to twodays, whereas printing plates having hydrophilic layers sealed bychromic acid in accordance with the present invention, retain their ingplates.

sodium zirconium hexafluoride (Na ZrF potassium zir- V coniumpentafluoride (KZrF sodium zirconium pentafluoride (NaZrF titaniumtetrafluoride (TiF potas- I sium titanium hexafluoride (K TiF hafniumtetrafluoride (HfF potassium hafnium hexafluoride (K HfF and sodiumhafnium hexafluoride (NaHfF In addition to the acids and alkali metalsalts indicated above the alkaline earth metal salts and ammonium saltsofv may be utilized to form the hydrophilic layer, although treatmentwith the latter salts tends to produce plates having more limited shelflife.

The transition metal fluorides which may be utilized in accordance withthe present invention thus include titanium tetrafluoride (TiF zirconiumtetrafl'uor'ide (ZrF hafnium tetrafluoride (HfF and pentaflu'oride's andhexafluorides having the formula Milt 1 F, in which M may be eitherhydrogen, alkali metal, alkaline earth metal or ammonium radicals, M2may be either a titanium, zirconium or hafnium cation, and rt is either5 or 6.

It is preferred to immerse the metallic base in an aqueous solutioncontaining from about 0.01% to 1% of the transition metal fluoride. Thetemperature of the fluoride treating bath is maintained within the rangeof from about 70 to 180 F., the pH of the solution being regulatedwithin the range of from about 3.5 to 5. The time of immersion is notcritical and preferably is Varied from as little as five seconds to asmuch as five minutes. It will be understood that, within the rangesindicated above, the temperature, time and concentration of thetransition metal fluoride may be varied to produce optimum results. Ifdesired, a soluble zinc salt may also be included in the transitionmetal fluoride solution in the manner described in application SerialNo. 29,133, filed May 16, 1960, now abandoned.

The hydrophilic layer thus produced is sealed by treatment with chromicacid Which material may, if desired, be incorporated in the'transitionmetal fluoride treating bath in an amount of from about 0.001% to 2.5%but as indicated hereinafter is preferably incorporated in a separatetreatment bath subsequent to formation of the hydrophilic layer. Theseparate aqueous chromic acid treatment bath contains from about 0.001%to 2.5%, preferably, about 0.02%, Cr and is maintained at a temperatureof from about 70 F. to 180 F-., preferably at about 160. F. The metallicbase having the hydrophilic layer thereon is immersed in the chromicacid sealing bath for a period which may vary from about one minute tonine minutes, preferably lasting about three minutes.

The chromic acid treatment seals the hydrophilic layer, therebyminimizing moisture absorption and producing the improved temperatureand humidity stability characteristics described hereinabove. The exactmeehanism by which the transition metal fluoride and chromicacid reactto produce a sealed hydrophilic layer on the ain minum or other metallicsubstrate is not known; It is possible that the chromic acid forms achromate layer atop a hydrophilic fluoride layer formed on the metallicsubstrate, sealing the pores in the fluoride coating. Alternatively, thetransition metal fluoride may be bound directly to the metallic plateand crossli'nked by the dchydr'ating action of chromic acid according tothe fol? lowing equations illustrating the possible reaction mecha anismwhen hydrofluozirconic acid is utilized to form the hydrophilic layer:

Surface 5, Surface (Dehyiration) layer.

It will be understood that the above reaction mechanisms providepossible explanations of the operation of the invention but are notintended to be limiting thereof.

The photosensitive emulsion coated on the printing plate comprises anyof the commonly available lightsensitive materials useful forlithographic purposes, such as the light-sensitive diazo resins,bichromated albumin, gum, casein, furfural-acetone condensationproducts. or cinnamylresinous materials, utilized alone or incombination. It is preferred, however, to utilize a lightsensitive diazoresin coating as the photosensitive emul sion applied atop the chromicacid sealed hydrophilic It has unexpectedly been found that such acoating is more strongly bonded to such layer than to previously knownhydrophilic layers. Diazo sensitized printing plates prepared accordingto the invention have thus provided extremely longpress runs, upwards of10,000 copies being produced without difficulty.

Any of the well known light-sensitive diazo materials, such as thosedisclosed in column 5 of U.S. Patent No. 2,937,085, in column 2 of- U.S.Patent No. 2,649,373 or referred to in column 10 of U.S. Patent No.2,714,- 066, may be utilized. Any of these or other conventional diazosensitizers, which are negative-acting, may be treated in the mannerdisclosed in copending application Serial No. 126,502, filed on July 25,1961, now U.S. Patent No. 3,113,023, if desired, to provide apositiveacting plate.

A typical light-sensitive diazo'resin useful in the practice of thepresent invention is the condensation product of paraformaldehyde andparadiazodiphenylamine. Employing this resin', the diazo coating maycomprise, for example, 1% of the resin dispersed in a saponin solution.

The thus sensitized plate is thereafter exposed image wise to actiniclight to form a permanent oleophilic image. The latent image produced byexposure is developed by means of a suitlable lacquer or otherdeveloper, producing an oleophilic image and leaving hydrophilicnon-image portions exposed on the underlying h'ydro philic layer. Theplate can then be placed on a press and a large number of copies madetherefrom.

It is preferred that, prior to treatment with the transition metalfluoride, the surface ofv the metallic base, e.g., aluminum, bedegreased and chemically activated in order that a more stronglyadhering image can be obtained. Consequently, the aluminum is preferablysubjected to pretreatment with an alkali degreasing agent, an acid etch,a desmutting reagent, and with a further acid reagent containing an acidsuch as phosphoric acid, chromic acid, nitric acid, sulphuric. acid oroxalic acid, which activates the aluminum surface, and increases itsreceptivity for the subsequent formation of the hydrophilic layerthereon. I

Typical acid etching treatments known in the art, such as thosedescribed in U.S. Patent No. 2,882,153, may be employed. If a grainedplate is desired the aluminum base is not etched but is rather grainedby suitable mechanical means, e.g., by rubbing with an abrasive,sandblasting or brushing with a wire, nylon or hair brush. Details ofsuch mechanical graining procedures are found in the prior art, e.g.,see U.S. Patent No. 2,882,155,

It is preferred to employ either phosphoric or oxalic acid in the acidactivating bath in a concentration in the range of from about 0.01% to5% by weight, optimum results being obtained when employing such acidsin concentration ranges of from about'0.2% to 1%. The time ofimmersionin the acid bath, which is maintained at between about 50 F.and F., preferably at about 65 F., is varied between about one secondand three minutes, with'five to ten seconds giving good results,depending'on the concentration of the bath. The time, temperature andconcentration of such bath may be chosen as desired within the indicatedlimits to produce optimum results.

The following examples are given for illustrative purposes; it will beunderstood that the invention is not limited to these examples.

Example I A sheet of 3S aluminum (99% purity) was degreased and etchedin a solution of trisodium phosphate at 160 F. for a period of threeminutes. The platelwa's thereafter rinsed in tap water for three minutesat room temperature and then immersed in a desmut solution for 10 toseconds, the solution containing 15% sulphuric acid and 2.6% chromicacid. The plate was then removed and rinsed in running tap water forthree minutes at room temperature.

The pretreated plate was immersed in a 0.18% solution (pl-i=4) ofpotassium zirconium hexafluoride for three minutes. The solution wasmaintained at a temperature of from 150 F. to 160 F. during theimmersion. Immediately after removal from the hexafiuoride treatingsolution the plate was immersed in a chromic acid bath containing .03%CrO which bath was at 150 F. to 160 F. After three minutes in the latterbath, the plate was removed, rinsed with water, dried and sensitized byapplying a solution of a diazo resin to both sides of the aluminumsheet. The diazo resin employed was the condensation product ofparaformaldehyde and paradiazodiphenylamine (containing four parts offormaldehyde per thirty parts of paradiazodiphenylamine). The coatedplate retained approximately 0.25 cc. of the diazo resin coatingsolution per side and, after drying, was ready for use.

Upon exposure to a source of ultra-violet light through a negative, astrong, water-insoluble image was formed on the surface of the plate.After redeveloping the image five times, the plate was placed on aprinting press and over 10,000 sharp and clear copies run.

Example II Upon following the procedure described in Example I,substituting titanium tetrafluoride for the potassium zirconiumhexafluoride employed to form the hydrophilic layer on the aluminumsurface, similar results were obtained. and clear distinct copies wereformed upon printing with the resulting planographic printing plate.

Example Ill An aluminum plate was degreased, etched and'rinsed in themanner described in Example I. The plate was then immersed in a desmutsolution containing 6% sulphuric acid and 1% chromic acid.

6 to 1% of a transition metal fluoride selected from the groupconsisting of TiF ZrF HfF and a. compound having the formula M M F inwhich M is a cation selected-from the group consisting of hydrogen, analkali metal, an alkaline earth metal and ammonium, M is selected fromthe group consisting of Ti, Zr and Hf, and n is an integer from 5 to 6,at temperatures between 70 F. and 180 F., to form a hydrophilic layerthereon; subsequently sealing said layer by reacting the same with asolution containing from 0.001% to 2.5 chromic acid at temperaturesbetween 70 F. and 180 R; and applying a light-sensitive diazo resincoating over the resulting sealed hydrophilic layer.

2. The method for preparing a pre-sensitized'planographic printing plateas defined in claim 1, including the furtherfstep of exposing the thustreated plate to actinic light and treating the exposed plate to producean adhering oleophilic image thereon.

3. The method defined in claim 1, in which said transition metalfluoride is a zirconium hexafluoride.

4. The method defined in claim 1, in which said transition metalfluoride is zirconium tetrafluoride.

SJA presensitized planographic printing plate, produced by the methoddefined in claim 1.

6. The presensitized planographic printing plate as defined in claim 5,in which said transitionmetal fluoride is a zirconium hexafiuoride. i

7. The presensitized planographic printing plate as defined in claim 5,in which said transition metal fluoride is zirconium tetrafluoride.

8. A method for preparing a presensitized planographic printing platecomprising forming. a hydrophilic layer on at least one surface of adegreased aluminum sheet by treating the same with a solution of from0.01% to 1% of a transition metal fluoride selected from the groupconsisting of TiF ZrF H11 and a compound having the formula M M F inwhich M is a cation selected from the group consisting of hydrogen, analkali metal, an alkaline earthmetal and. ammonium, M is selected fromthe group consisting of Ti, Zr and Hf, and n is an integer of from 5 to6, said solution being maintained at a pH between 3.5 and 5 and at atemperature between 70 F. and 180 F., for a period of from five secondsto five minutes, subsequently sealing said hydrophilic layer bytreatment with a solution of from 0.001% to 2.5% chromic acid at atemperature between 70 F. and 180 F. for a period of from one to nineminutes, and thereafter applying a light sensitive diazo resin coatingover said hydrophilic layer.

,After rinsing the pre-treated plate it was immersed in a 0.06% solutionof hydrofluozirconic acid at 70 to 90 F. for three minutes. Thehydrophilic layer thus formed was thereafter sealed by immersing thetreated plate in a bath containing a mixture of 0.03% chromic acid and0.007% hydrofluozirconic acid.

The thus sealed hydrophilic layer was coated with the light-sensitivediazo resin coating, exposed and treated in the manner described inExample I above. The resulting printing plate produced clear, sharpcopies upon printing. a

The present invention thereby provides a method for preparingplanographic printing plates, and the resulting plates, which are stableunder relatively high humidity and temperature conditions and whichprovide long press runs. Since various changes may be made in carryingout the above method and in the structure of the resulting printingplate without departing from the scope of the invention, it is intendedthat all matter contained in the above description shall be interpretedas illustrative and not in a limiting sense.

What is claimed is;

1. A method for preparing a pre-sensitized planographic printing platecomprising, treating an aluminum surface with an aqueous solutioncontaining from 0.01%

9. The method defined in claim 8, in which said transisurface thereon,subsequently sealing said hydrophilic surface by treating the plate witha chromic acid bath containing from 0.001% to 2.5% CrO at a temperaturebetween 70 F. and F., applying a light-sensitive diazo resin coatingover the resulting sealed hydrophilic layer, said diazo resin comprisingthe condensation product of paraformaldehyde and paradiazodiphenylamine,exposing the thus sensitized plate to actinic light and treating theexposed plate to produce an adhering oleophilic image thereon.

References Cited in the file of this patent UNITED STATES PATENTS2,922,715 Gumbinner Jan. 26, 1960 2,946,683 Mellan et a1 July 26, 19603,073,723 Deal a a1 Jan; 15, 1963

11. A METHOD OF MAKING AN ALUMINUM BASE PLANOGRAPHIC PRINTING PLATECOMPRISING TREATING A DEGREASED ALUMINUM SHEET WITH AN AQUEOUS SOLUTIONOF FROM 0.01% TO 1% POTASSIUM ZIRCONIUM HEXAFLUORIDE AT A TEMPERATUREBETWEEN 70*F. AND 180*F. TO FORM A HYDROPHILIC SURFACE THEREON,SUBSEQUENTLY SEALING SAID HYDROPHILLIC SURFACE BY TREATING THE PLATEWITH A CHROMIC ACID BATH CONTAINING FROM 0.001% TO 2.5% CRO3 AT ATEMPERATURE BETWEEN 70*F. AND 180*F., APPLYING A LIGHT-SENSITIVE DIAZORESIN COATING OVER THE RESULTING SEALED HYDROPHILIC LAYER, SAID DIAZORESIN COMPRISING THE CONDENSATION PRODUCT OF PARAFORMALDEHYDE ANDPARADIAZODIPHENYLAMINE, EXPOSING THE THUS SENSITIZED PLATE TO ACTINICLIGHT AND TREATING THE EXPOSED PLATE TO PRODUCE AN ADHERING OLEOPHILICIMAGE THEREON.